[Cake] Cobalt Initial Target Value

[Jonathan Morton]

> On 15 Apr, 2017, at 11:50, Harsh Lara <harshapplefan at gmail.com> wrote:
> 
> I was reading the code for the Linux implementation of COBALT. I wanted to know where the target queue delay is being set initially in the code.

Both ‘target’ and ‘interval’ are treated as parameters to COBALT in the same way as for Codel.  They are thus normally initialised in cake_set_rate(), rather than in COBALT itself.

> Also, is there any recommended value for target?

As a rule of thumb, set ‘interval’ to your expected average path RTT (assume 100ms for general Internet traffic) and ‘target’ to 1/20th of that.

However, ‘target’ should also be high enough to permit ordinary serialisation delay of an MTU-sized packet without triggering the AQM.  This clamping is part of what cake_set_rate() does, ensuring ‘target' corresponds to at least 1.5 MTUs at the shaped rate.

 - Jonathan Morton